Thread-lock.



A. LATHAM.

THREAD LocK. i

APFLICATOM FILED JULY 15, |915.

Patented May 15, 1917.

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ALBERT LATHAM, 0F BEVERLY, MASSACHUSETTS, ASSIGNOR TO UNITED SHOE MACHINERY COMPANY, OF PATERSON, NEW JERSEY, A CORPORATION OF NEW JERSEY.

THREAD-LOCK.

Specicaton of Letters Patent. v

Patented May 15, 1917.

' Application filed July 15, 1915. Serial No. 39,993.

To all whom it may concern.'

Be it known that I, ALBERT LATHAM, a citizen of the United States, residing at Beverly, in the county of Essex and State of Massachusetts, have invented certain new and useful mprovements in Thread-Locks; and I do hereby declare the following to be a full, clear, and exact description ofthe invention, such as will enable others skilled in the art to which it appertains to make and use the same. i

The present invention' relates to an improvement in thread locks for lock-stitch sewing machines. The thread lock of lockstitch sewing machines operates at the requisite times to clamp the thread, while the take-up draws the loop against the locking thread and thereby completes theV stitch. The formation of uniform stitches under the necessary tension requires the exertion of a uniform pressure on the thread by the thread. lock; it is consequently necessary that the surface of the thread clamping end of thethread lock be always smooth and free from grooves worn therein by the constant engagement of the thread lock with the thread. For this reason thread locks are made of steel and hardened. Yet, notwithstanding the hardness of the thread clamping end of the-thread lock, the friction to which the thread clamping` surface thereof is subjected during` its thread clamping function, is such as to cause the clamping surface to wear; this wearing of the clamping surface of the threadclamping end of the thread lock results in improper clamping and, consequently, the formation of imperfect stitches. This necessitates the removal of the worn part and the substitution of a new part therefor, and as these locks have hitherto been constructed, 'the wearing of the thread clamping end vof the lock has necessitated the replacement of the whole lock.

One object of the present invention is, therefore, the production of a thread lool: the clamping surfaceof which, when worn, may be replaced by a new thread clamping surface without the necessityof replacing the whole thread lock. In accordance with this object, the thread clamping end of the thread lock Ais provided with a brake shoe or wear plate which can be readily removed and replaced by a new plate. The invention consists further in improved details of construction and arrangement of parts of thread locks for lock-stitch shoe sewing machines, which will be readily apparent to those skilledin the art; and to this end,'the invention consists of the improved thread loclr hereinafter described and particularly pointed out in the appended claims.

The present invention will be clearly understood from an inspection of the accompanying drawings, in which Figure 1 is a side elevation of so much of a vlock-stitch shoe'sewing machine as is necessary to disclose the application of the improved thread loclr thereto; Fig. 9. is an enlarged side elevation, partly in section, of the thread lock; Fig. 3 is a perspective view of the clamping end of the thread look, and Fig. 4t is a perspective view of the removable wear plate.

The lock-stitch shoe sewing machine to which the improved thread lock is applied comprises a needle 10, an awl12, a work support 14, a fixed bobbin casing 16 and its assooiatedrotary hook 18, atake-up 20, an auxiliary take-up' 22, a pull-oif 24, a thread truck 26, and other parts' usual and custoinary in this type of machine, some of which will be described in the following disclosure of the present invention. The thread 28 is fed to the needle inv the usual manner. The parts just enumerated and their mode of loperation are fully described in Fred Ashworths pending application for Letters Patent, Serial No. 585,116, filed October 3, 1910, to which reference is had by permission.

The improved thread lock consists of a lever 30, `which is pivotally mounted at 82 on the frame of the machine and is actuated by a cam shaft 34C thro-ugh suitable connections at requisite times to clamp the thread while the take-'up is taking up the slack of the thread after the rotary hook has looped the thread around the fixed bobbincasing, and thereby formed the loop,- the preliminary step in the formation of theloclestitch. The freeend ofthe thread locking lever constitutes its clamping or thread engaging end and is concaved at 36 in conformity with the periphery of the thread truck 26, around which the thread passes as it is fed to the needle, and against which the thread is clamped at the requisite times. Mounted upon the clamping end of the thread locking lever is a brake shoe or wear plate 38, the thread engaging surface 10 of which is curved in conformity with the concave surface of the' clamping end of the lever. The wear plate is made of tempered steel and its construction and that of the clamping end of the lever are such that it may be readily placed in operative position on the lever and removed therefrom when worn, and yet, when in operative position, be held against lateral and longitudinal displacement. The arrangementof parts by which these results are attained consists in the following construction: The clamping end of the lever is slotted longitudinally at 42 and the opposite extremities 44 and 46 of the clamping end are arranged-in an acute, angular relation with the concaved surface 36; the opposite ends 48 and 50 of the wear plate are arranged similarly to the extremities 44 and 46. Each angularly disposed end of the plate is provided with two parallel slits which divide it into three divisions. Each middle division 52 o-f the ends of the wear plate is bent inwardly beyond the surface of the outer divisions, so as to form an inwardly projecting ear or tongue. By constructing the clamping end of the lever and the wear plate in the manner just described, they are furnished with coperating parts, so that the plate may be readily sprung into and removed from operative position on the clamping end of the lever. The `resiliency of the material of which the plate iscomposed facilitates its positioning and removal. When the plate is in operative position, as is clearly shown in Fig. 2, the angularly disposed ends of the plate coperating with the similarly disposed extremities of the clamping end of the lever, prevent longitudinal displacement; and the inwardly projecting tongues entering the opposite ends of the longitudinal slot 42 in the lever, prevent lateral displacement.

The scope of the present invention having been indicated and a specific embodiment having been described, what l claim and desire to secure by Letters Patent is:

l. A thread lock for lock-stitch sewing machines, `the stitch formingv devices of which include a yneedle and a take-up, said thread lock consisting ofa lever provided on its thread clamping end with a wear plate, said lever and platehaving'coperating portions whereby said plate may be-sprung into operative position on the lever.

2. A thread lock for'lock-stitch sewing machines, the stitch forming devices `of which include a needle and a take-up, said thread lock consisting of a lever and a wear plate located on the thread clamping end of the lever, said plate being composed of resilient material by virtue of which it may be sprung into operative position on the lever.

3. A thread lock for lock-stitch sewing machines, ythe stitch forming devices of which include a needle and a take-up, said thread locking device comprising a lever, a slot in the thread clamping end of the lever, and a wear plate mounted on `the clamping end of the lever having ears adapted to enter the slot and prevent lateral displacement of the wear plate.

4. A thread lock for loclr-stitch sewing machines, the stitch forming devices of which include a needle and a take-up, said thread locking device consisting of a lever having a wear plate mounted on the clamping end thereof, said lever and plate having cooperating portions whereby when said plate is sprung into operative position on the lever, it is held against longitudinal and lateral displacement thereon.

5. A thread -lock for loclrstitch sewing machines, the stitch forming devices of which include a needle and a take-up, said thread locking device consisting of a lever having a concave surface at its thread clamping end provided with a longitudinal slot, the eX- tremities of the clamping end of the lever being arranged in acute angular relation with said surface, and a wear plate mounted on the clamping end of the lever having a clamping surface shaped in conformity with the surface of the lever, the ends of the plate being arranged similarly to the extremities of the clamping end of the lover and being provided with inwardly projecting tongues adapted to enter the slot in the clamping end of the lever.

6. A thread lock for lock-stitch sewing machines, the stitch forming devices of which include a needle and a take-up, said thread locking device comprising a lever having a wear plate mounted on the clamping end thereof, said lever and plate having coperating recesses and projections whereby, when said plate is in operative position on the lever, the projections are adapted to be inI engagement with the recesses to hold the plate against displacement.

ALBERT LATHAM.

Copies of this .patent may 'be obtained for ve cents each, by addressing the Commissioner of Patents,

- i y f Washington, ID. C. 

